Predissociation linewidths in O2 B 3Σu− (v=0,2)

Abstract

Using laser‐induced fluorescence techniques applied to Schumann–Runge absorption transitions from vibrationally excited O₂(X³Σ_g⁻), we have measured the rotational and fine‐structure level‐specific linewidths in v=0 and v=2 of the B³Σ_u⁻ state. These linewidths represent the first measurement of fine‐structure level‐specific predissociation rates in B³Σ_u⁻(v≤10), and they are found to vary considerably among the various rotational and fine‐structure levels, encompassing a range of 0.09–0.34 cm⁻¹ in v=0, N’≤36, and 0.4–1.4 cm⁻¹ in v=2, N’≤24. Orbit‐rotational coupling in the B³Σ_u⁻–³Π_u interaction, in addition to spin‐orbit coupling in the B³Σ_u⁻–¹Π_u, −³Π_u, −⁵Π_u interactions, is found to be crucial to explaining the relative predissociation rates among the fine‐structure levels, even in low rotational levels. Measurements were made in the (v’,v‘)=(0,9), (0,10), (0,21), (2,10), and (2,22) Schumann–Runge [B³Σ_u⁻(v’)←X³Σ_g⁻(v‘)] bands without presumption as to the molecular constants in either the X or B states. The use of high ground state vibrational levels as a starting point for the photoexcitation measurements produces a spectral separation among the previously blended triplet components of the absorption lines. All lines in these bands are found to be broadened by predissociation, with those terminating in v’=0 and in the N’=J’−1 (F’₁) levels exhibiting the smallest effect.